The overall goal of this project is to understand how retroviruses adversely affect the central nervous system. We are utilizing the mouse as an animal model and have focused our attention on two coisogenic viruses FrCas, which causes an acute non-inflammatory spongiform encephalomyelopathy, and F43 which is avirulent. The two viruses differ in the sequence of their envelope proteins and studies in previous years revealed that the neurovirulence of FrCas was associated with folding instability of its envelope protein and induction of Endoplasmic Reticulum Stress. It is for these reasons that we now suspect that the brain disease induced by FrCasE and related murine retroviruses represents a virus-induced protein folding disease.[unreadable] [unreadable] Formal genetic linkage studies to test the connection between ER stress and neurovirulence are near completion. A series of viruses were constructed which carry chimeric envelope genes containing sequences from FrCasE and F43 all on the same genetic background. The induction of ER stress, as measured by the upregulation of mRNA encoding ER chaperones, was detectable only in those viruses carrying FrCas sequences within the N-terminal third of the viral envelope protein. Likewise, it was only this group of viruses that also induced spongiform neurodegeneration in the brain. Finally the degree of neurovirulence as measured by the severity and distribution of lesions in the brain was directly correlated with the state of folding instability as measured by steady-state binding of the ER chaperone BiP to the viral envelope protein. These results provide strong evidence that misfolding of this viral protein has a direct bearing on the capacity of the virus to precipitate neuropathology. [unreadable] [unreadable] A collaborative study with Drs. Nico Dantuma, Karolinska Institute, and Sarah Tabrizi, University College London, detailed in the 2006 Annual Report, investigated the role of the Ubiquitin-Proteasome System (UPS) in the pathogenesis of TSE diseases. These studies revealed that PrPsc oligomers inhibit the Ubiquitin-Proteasome system by specifically interfering with caspase-like and chymotrypsin-like protease activity (beta1 and 5 proteolytic active sites) of the 20S core. In vivo studies carried out at the Rocky Mountain Laboratories confirmed UPS dysfunction occurred in the brains of mice inoculated with several strains of mouse-adapted prion agents. revealed inhibition of the UPS in the brains of mice with clinical neurologic disease that at least during the clinical phase of the neurodegenerative disease induced by several strains of mouse scrapie. This study represents the first clear evidence that the pathogenesis of TSE (prion) diseases may be linked to inhibition by the abnormally folded protein PrPsc of specific catalytic subunits of the proteasome. [unreadable] [unreadable] In collaboration with Dr. Michael Oldstone, Scripps Research Institute, we explored the role of IL10 in controlling persistent retroviral infection. His laboratory found that IL10 expression in mice persistently infected with Lymphocytic Choriomeningitis Virus (LCMV) was largely responsible for inhibition of the anti-viral adaptive immune responses and consequent viral clearance. We were interested in determining if IL10 might also be involved in maintaining retroviral persistence. Studies were carried out in mice persistently infected with the mouse gamma-retrovirus F43. As was the case for LCMV, IL10 mRNA was upregulated in spleens of infected mice. However, unlike LCMV, we found no evidence that repeated treatments with an antibody to IL10- receptor impacted viral burden. These studies indicate the findings in LCMV may not be applicable to control of retroviral infections.